(i) Field of the Invention
This invention relates to bipolar electrodes. it also relates to modular bipolar electrode assemblies which are especially adapted for use in a bipolar electrolytic cell of the type used for the manufacture of chlorates, perchlorates, persulphates, or hydroxides and to the bipolar electrolytic cell so provided.
(ii) Description of the Prior Art
Bipolar electrolytic cells have been mainly successful, but improvements have been desired for the bipolar electrodes per se.
There are many forms of bipolar electrodes which are essential elements of a bipolar electrolytic cell. For example, U.S. Pat. No. 4,089,771 issued May 16, 1978 to H. B. Westerlund, provided a bipolar electrode including a cathodic element, the exposed outer surface of which was of an activated porous titanium nature. The central core of the cathodic element was formed of a titanium sheet, which extended outwardly from an edge of the cathode to provide the anode.
U.S. Pat. No. 4,116,807 patented Sep. 26, 1978 by E. J. Peters, provided a face-to-face bipolar electrode which included explosion bonded solid metallic strips between the two blackplates of a bipolar electrode to provide the essential electrical and mechanical connection therebetween.
U.S. Pat. No. 4,414,088 issued Nov. 8, 1983 to J. B. Ford, provided a bipolar electrode including anodic and cathodic metal layers intimately and integrally connected by explosive binding, to opposite faces of an electrically-conducting metal layer.
Other patents provided bipolar electrodes which included a central conductor to which parallel, spaced-apart anodes and cathodes were electrically connected on opposite sides thereof. In these prior patents, assembly was required whereby the anode was to be facing the cathode and viceversa. Great care was necessary in assembling such bipolar electrodes to avoid causing electrical short circuits.
In another type of bipolar electrode, the anode and cathode parts were each made from the same material. The anode part had and electrocatalytic active coating, or both parts consisted of alloys having the same main components.
U.S. Pat. No. 4,098,671 patented on Jul. 4, 1978 by H. B. Westerlund, provided several embodiments of bipolar electrodes. In one embodiment, the cathode was connected to the anode in an edge-to-edge orientation by means of an upstanding, "U"-shaped (in cross-section) median electrode. The connection was by means of welding.
Canadian Patent No. 990,681 patented Jun. 8, 1976 by Pierre Bouy et al, provided a bipolar electrode having an anodically active part comprising a film-forming metal covered with a conducting layer which was inert to electrolytes, and a cathodically-active part comprising a metal which could be used cathodically. The anodically and cathodically active parts were separated in space and were connected together by an electrical connection. The two electrolytically-active parts were apertured, the electrical connection between them being made through the contact formed within a plurality of bonded members produced by plating a metal which can be used cathodically with a film-forming metal. The bonded members were part of a sealing partition separating the two electrolytically active parts.
Canadian Patent No. 1,032,892 patented Jun. 13, 1978 by H. B. Westerlund, provided an improvement in such electrode by providing electrically-insulating spacer elements projecting from both side faces of the cathode.
Canadian Patent No. 1,053,177 patented Apr. 24, 1979 by Maomi Seko, et al, provided a bipolar electrolytic cell including a partition wall made of explosion-bonded titanium plate and iron plate which partitioned the cell into an anode chamber and a cathode chamber. The anode was formed of a titanium substrate having platinum group metal oxides coated thereon, which was connected electrically to the titanium of the partition wall in a manner such that space was provided between the anode and the titanium of the partition wall. The cathode was formed of iron which was connected electrically to the iron of the partition wall in a manner such that space was provided between the cathode and the iron of the partition wall.
Canadian Patent No. 1,094,981 patented Jan. 3, 1981 by James D. McGilvery, provided a bipolar electrode including a layer of a passivatable metal, typically titanium, having a conductive anolyte-resistant anode surface, a layer of iron or an alloy thereof, typically steel, providing the cathode, and a layer of a metal or alloy thereof resistant to atomic hydrogen flow positioned between, and in electrical contact with, the iron or alloy thereof and the passivatable metal layer.
Canadian Patent No. 1,128,002 patented Jul. 20, 1982 by Ronald Dickson, et al, provided an electrode for use in a diaphragm or membrane cell having a gap of a given width between adjacent diaphragms or membranes. The electrode included two electrode sheets disposed substantially parallel to each other, and an elongate current feeder post located between, and directly attached to, the sheets along their centre line. The sheets were thus resiliently movable towards one another for insertion into the gap and springable outwardly when in the gap. The two electrode sheets included a web portion and on each side of the web portion were integral, substantially planar portions having an anodically active outer layer on at least part of their surfaces. The two web portions were directly attached to opposite sides of the current feeder post and included two flanges which were splayed outwardly from the current feeder post so that the two free edges of the planar portions of the electrodes were spaced wider apart than the parts of planar portions closest to the connection line with the flange. The free edges were spaced further apart than the width of the gap between the diaphragms or membranes. The electrode working sheets could be imperforate or foraminous.
Canadian Patent no. 1,143,334 patented Mar. 22, 1983 by Kin Seto, et al, provided a bipolar electrode assembly including first and second base plates disposed in parallel relationship at a distance from each other, a number of spaced-apart pairs of perforated metal electrode plates projecting from the first base plate at essentially right angle thereto in the direction of but short of the distance to the second base plate, and an equal number of metal electrode plates projecting from the second base plate in the direction of but short of the distance to the first base plate. Each one of the metal electrode plates which projected from the second base plate projected, and was sandwiched between, the two members of a corresponding pair of perforated metal electrode plates and has its opposite faces insulated from the individual members by a thin film of an electrically-insulating material carrying perforations similar and aligned with those of the perforated electrodes.
Canadian patent No. 1,143,335 patented Mar. 22, 1983 by Kine Seto, et al, provided a bipolar electrode assembly including first and second base plate disposed in parallel relationship at a distance from each other, at least one row of equidistantly spaced-apart finger-like metal cathodes projecting from the first base plate in the direction of, but short of the distance to the second base plate. The cathodes in each row were in a same plane essentially perpendicular to the base plates. For each row of finger-like metal cathodes, a corresponding coplanar row of finger-like metal anodes projected from the second base plate in the direction of, but short of, the distance to the first base plate. The anodes and cathodes of corresponding coplanar rows of anodes and the cathodes were interdigitated and were insulated from each other by a thin layer of a non-electrically conductive insulating material.
Swedish Patent No. 8100968 of Kemanord AB., provided a compound electrode for electrolysis, which includes several parts which were connected to each other mechanically in such a away that a high and even pressure was applied. The electrode construction included five parallel connected parts. Each part comprised a U-shaped component, and a T-shaped component. These components were shrink-welded together. The U-shaped parts were then connected to a plate.
The art has also provided bipolar electrodes which were coextensive plate-like in nature and which were connected edge-to-edge. One such bipolar electrode was described in Canadian Patent NO. 1,036,540 patented Aug. 15, 1978 by C. N. Raetzsch, Jr., et al. In that patent, the bipolar electrode included a plurality of sets, each set comprising a pair of spaced-apart cathode plates and a pair of spaced-apart anode plates. The pair of cathode plates were interconnected at one end at their edges by a conductor, and the pair of anode plates were likewise connected at one end at their edges by a conductor. These two conductors were interconnected by a conducting means. Such conducting means included an interposed metal member of less height than the height of the anode and cathode plates, and upper and lower insulating members. The other open end of the pair of anode plates was secured within two arms of an "H" profile insulating member, and the other arm of the "H" profile secured the open ends of a pair of cathode plates. Thus, the bipolar set includes the sequence: an anode; an insulator; a cathode; a conductor; an anode; an insulator; a cathode; and a conductor.
Another such bipolar electrode was described in canadian Patent No. 1,220,165 patented Apr. 7, 1987 by C. N. Raetzsch, Jr. In that patent a bipolar electrode was provided which was a single, unitary blade having an anodic portion and a cathodic portion, formed of titanium, or a titanium/yttrium alloy, with the cathode portion, which faced an anode portion, being perforated.
Still another such bipolar electrode was disclosed in Canadian Patent No. 1,230,081 patented Dec. 8, 1987 by P. Fabian, et al. In that patent, a bipolar electrode was provided having a flat plate-like shape, including an anode part made of a first material, a cathode part made of a second material, and a generally integral, pre-prefabricated intermediate piece having the shape of a strip whose thickness generally corresponded to the thickness of the anode part and of the cathode part. The strip was so positioned that its surfaces were generally co-planar with those of the anode and cathode parts, while side edge portions of the strip abutted against the respective one of the anode and cathode parts. the intermediate piece was comprised of a first side section and of a second side section, the side sections adjoining each other along an abutment joint extending longitudinally of the intermediate piece. The first section was made of a material having generally the same composition as the material, and the second section was made of a material having generally the same composition as the second material. A first abutment weld was provided between the first side section and the anode part, and a second abutment weld was provided between the first side section and the cathode part. Thus, a generally integral bipolar plate-like electrode was formed having the anode part and the cathode part made of different materials.
In all the above patented bipolar electrodes, problems still arose. A welded joint had problems due to the dissimilar metal properties. Explosion bonding developed interface problems, of which hydriding was the most typical. A lapped joint had several disadvantages, namely: the extra material cost due to the overlay; the increased thickness of the module; and problems with securing the joint without suffering dimensional instability. A bipolar electrode having a U-shaped profile which spaced the electrodes and blocked current leakage between the cells, nevertheless also lengthened the path of the current. Such lengthening of the current path required an increase in the voltage, which increased the cost of production.